Fractionation trays are devices to bring vapor and liquid phases into contact during fractional distillation, also they are widely used in the petrochemical and petroleum refining industries to promote the multistage vapor-liquid contacting performed in fractionation columns. The normal configuration of a fractionation column includes about 10 to 120 individual trays. Normally each tray is the same. The trays are mounted horizontally at uniform vertical distances referred to as the tray spacing of the column. This distance may vary within different parts of the column but is normally considered constant.
The trays must be supported within the surrounding pressure vessel, referred to as the column. This is often done by support structures attached to the inside surface of the column. These structures, referred to in the art as rings, must be moved or replaced when the tray spacing in a column is changed. This can occur when it is desired to increase the number of trays in the column.